Atypical squamous cells (ASC) are abnormal cells found on a Pap test, but the reason for the abnormalities is not known. The causes of ASC can include infection and inflammation.

ASC is further classified as:

• ASC of undetermined significance (ASC-US).
• ASC but cannot exclude high-grade squamous intraepithelial lesion (HSIL) (ASC-H).